1. Field of the Invention
The present invention relates to a paper feeding device and an image forming apparatus and, in particular, relates to drive transmission mechanisms for a paper feeding roller used in paper feeding operation.
2. Description of the Related Art
In an apparatus that can perform image forming by electro-photographic copying or by discharging ink droplets, a recording sheet is used as one of the recording media to bear images.
The recording sheet is delivered by a paper feeding roller from a placing portion of a paper feed tray detachably mounted in the image forming apparatus and is conveyed toward an image transferring position or a printing position.
While the paper feeding roller is rotated by a driving force that is transmitted from a driving source provided within the image forming apparatus, the paper feeding roller is not always used being coupled to a drive transmission mechanism from the driving source at all times.
That is, if the paper feed tray that is used to house paper is configured to be removable from the image forming apparatus when in paper replenishment or maintenance, a coupling mechanism that can select a state of drive transmission between the driving source side and the paper feeding roller side of the drive transmission mechanism may be used.
As for the coupling mechanism, known is a technology that uses a system similar to what is called a dog clutch that includes transmission rods or the like that fit in serrated teeth or recessed teeth which are provided on each shaft end of a rotating shaft on the paper feeding roller side and a transmission shaft on the driving source side and can mesh with each other.
As one example of the coupling mechanism in the foregoing system, the following describes a type that uses the fitting of recessed teeth and transmission rods, for example.
It is configured that the rotating shaft on the paper feeding roller side is provided with a fitting member having serrated teeth and being biased toward the shaft end side, while the transmission shaft on the driving source side is disposed with transmission rods that can fit in the recessed teeth of the serrated teeth along the radial direction (for example, Japanese Patent Application Laid-open No. 2007-256497).
In the above-described configuration, if the phase of the recessed teeth on the rotating shaft side agrees with that of the transmission rods on the transmission shaft side, the drive transmission to the paper feeding roller is enabled via the coupling mechanism.
In the conventional technology, when the meshing phases of the serrated teeth or recessed teeth and the transmission rods do not agree with each other, the transmission rods collide with the projecting teeth of the coupling mechanism. In such a case, after a paper feed tray is attached, required is an alignment operation of meshing phases in which both are fitted at the time the phases thereof agree with each other by either rotating the transmission rods or rotating the fitting teeth portion.
In particular, when the paper feed tray is attached again such as after it is pulled out for paper replenishment or maintenance and inspection, the meshing phases that were in agreement before being pulled out may be broken up and may be in a state of discrepancy, and thus it often requires the alignment operation of meshing phases.
However, in the case that a paper-feeding start command that instructs the paper feeding roller to start rotating is output at the time the paper feed tray is attached, if the above-described alignment operation is performed, a time lag is produced between the time of the paper feed command and the actual start time of the paper feeding roller.
When such a time lag is produced, extra time is required until a recording sheet on which an image is formed can be obtained.
In view of the above-mentioned conventional problems, there is a need to provide a paper feeding device and an image forming apparatus that are provided with the configuration in which, at the time the paper feed tray is set and a paper-feeding start command is output, a time lag between the time of the command and the starting time of the paper feeding roller can be prevented from being produced.